Industrial plants for production of sugars, alcohols, industrial enzymes, medicaments and the like as well as different energy plants for production of renewable energy from biomass is usually based on the activity of microorganisms under either aerobic or anaerobic conditions in process tanks. Examples are the production of insulin and beverages by yeast under anaerobic conditions in fermentation tanks where the substrate is malt or molasses, or a similar agricultural plant product rich in carbohydrates.
The treatment of waste is another area widely accepted as a proven technology and extensively used. Also in this case microorganisms in aerobic/anaerobic process tanks digest the waste. However, not only municipal sewage waste but also a number of various industrial and agricultural wastes are also treated through microbiological means.
The microbial activity is based on the growth kinetics of the different groups of microorganisms involved and of the activity of a number of specific enzymes necessary to perform the biochemical processes. The overall result of the processes is microbial growth, substrate consumption, and product formation. However, enzymes and microorganisms may be inhibited by the main products or side products, which accumulate in the process tank or any other substance resulting from the microbial transformations of the substrate. Also substances in the biomass or the substrate in it self may hamper optimal performance of the bioreactor. Such inhibition may lead to a substantially lower microbial activity and thus substantially lower production and perhaps a complete break down of the microbial process if the inhibitory substances are not carefully controlled.
Such risks are usually avoided or controlled by managing the substrate loading or the organic loading rate, the rate being set to ensure a concentration of the critical component below levels unacceptable to the process. Other process parameters such as temperature, pH, salinity, media composition, and the microbial consortia employed may also be selected according to the process optima. However, managing the organic loading rate at low inputs to the bioreactors inevitably result in low product formation and a poor performance of the process in general. The control of the other process parameters such as temperature and pH compensates only partly for the inhibition by the inhibitory substance or substances. A direct control of the inhibitory substance at levels sub critical to the process is far the most effective control if possible.
It is often desirable to remove volatile components from microbial process tanks during continued operation of the process, i.e. the inhibitory substance is continuously removed yet the process and the microorganisms are left unaffected.
Generally, volatile components can be separated from a liquid by air stripping or vapor stripping, such as e.g. steam stripping of ammonia from aqueous solutions, or e.g. steam stripping of methanol.
Methods and systems for vapor stripping of volatile components from liquids comprise steps and means for producing a vapor of volatile components, such as ammonia, from the liquid. Typically, evaporation means requires energy from a suitable heating medium, typically a heating medium of high value such as e.g. electricity or combustion fuel, whereas available on-site heating media often are low-valued heating media such as cooling media comprising otherwise wasted heat from e.g. combustion of organic waste gases in an engine.
For effective removal of volatile components from liquids at atmospheric pressure, large amounts of steam or heat are required. Consequently, typical vapor stripping apparatus comprises large, energy consuming, and expensive components, which are not suited for small in-situ liquid treatment systems, such as system for treatment of liquids of manure at animal farming sites.
U.S. Pat. Nos. 5,385,646, 5,498,317, 5,643,420 and 5,779,861 disclose an apparatus and method for treating process condensate from a chemical production plant wherein contaminants are substantially removed from a condensate by steam stripping and subsequent rectification in a relatively low pressure stripping/-rectification tower. A portion of condensed overhead and scrubbing aqueous liquid-containing contaminants is returned to the top of the rectification section of the tower as reflux and the balance is withdrawn as a concentrated steam.
DE 43 24 410 C1 discloses a method of removing ammonia from waste aqueous liquid of a biological waste treatment plant, the method consisting of a two step process: a first step comprising stripping ammonia from the waste aqueous liquid by steam at atmospheric pressure, condensing said steam comprising stripped ammonia, and producing condensation heat for producing said steam; and a second step comprising rectifying said condensed steam comprising ammonia to at least 20% by weight of aqueous ammonia, said second step advantageously being carried out at a pressure above atmospheric pressure.